Process for the production of ketones



Patented Oct. 30, 1945 PROCESS FOR THE PRODUCTION OF KETONES Charles Weizmann, London, England No Drawing.

Application November 6, 1942,

Serial No. 464,789. In Great Britain April 11,

2 Claims.

The present invention relates to the manufacture of aliphatic ketones containing an even number of carbon atoms from ketones containing half the number of carbon atoms.

One of the methods for the self-condensation ofketones containing the system CH3-CO- or CH-. CO'consists in the treatment of the ketones with gaseous hydrochloric acid followed by treatment with alkali and distillation. this way, from acetone, e. g., mesityl oxide is obtained. It has been shown (Bull. Soc. chim., France,*49, 426) that in this reaction first a chloro-ketone is obtained which on subsequent treatment with alcoholic alkali loses hydrochloric acid and gives the desired tarp-unsaturated ketone:

While the first step of the process is comparatively simple from a technical point of view, the second one involves a number of operations and a loss of material.

It has now been found that such chloro-ketones and analogous bromo-ketones), containing a tertiary chloro-atom (or bromo-atom) in fl-position to the carbonyl group, lose one molecule of hydrochloric acid (or hydrobromic acid), when heated in presence of very small amounts (OJ-1%) of iodine: by simple distillation in chloro-ketone, and is dehydrated by the iodine, in well-known manner. It may be pointed out that this method has four distinct advantages over its previous forms: a

(a) It reduces the whole process to two operations.

(b) No loss of material is sustained; the hydrochloric acid is nearly completely recovered as such and can be used for further rondensation. (In the previous form of this process the hydrochloric acid which became linked to the ketone molecule was lost in the form of alkali chloride.)

presence of iodine, the desired lac-unsaturated ketone is obtained. It 'is even not necessary to isolate the chloro-ketone in a pure state; the crude product of interaction between the ketone and hydrochloric acid may be distilled in presence of iodine, so that the whole operation of conversion into the unsaturated ketone is reduced to a simple fractionation. y

The process according to this invention may be carried out as follows: Gaseous hydrochloric acid is dissolved in an excess of the ketone. After a suitable time, the mixture is distilled, the escaping hydrochloric acid being recovered and used for a new quantity of the ketone. The first fraction consists of unreacted ketone, containing the water formed during the reaction; when the fraction has been distilled ofi, iodine is added and the distillation continued. An additional quantity of hydrochloric acid and some more water distils over, followed by the unsaturated ketone.

The water in the second half of the distillation derives from some s-hydroxy-ketone, which had been formed along with the corresponding 5- (c) In none of the stages of the process is the addition of a solvent necessary.

(d) The phydroxy-ketone formed by direct ketolisation of the starting material is dehydrated to give the same unsaturated ketone by the same procedure. Using alkali for the removal of hydrochloric acid from the chloroketone, the ketol is not or not completely dehydrated; its dehydration must be efiected in a separate operation.

It is also possible, if desired, to isolate the chloro ketone, preferably by vacuum distillation and to decompose it in the desired manner by the process set out.

The following examples illustrate how the invention may. be carried out in practice, but it is to be understood that the invention is in no way limited to the details given in these examples.

Example 1 333 parts of gaseous hydrochloric acid are dissolved in .1000 parts of methyl-ethyl-ketone, the temperature being kept between 15 and 30 C. After standing for 48 hours, the brownish reaction product is distilled, the escaping gas being recovered in fresh methyl-ethyl-ketone. The first fraction of the distillate consists of the azeotropic mixture of water and methyl-ethyl-ketone, the second one of pure methyl-ethyl-ketone. When the distillation temperature has reached C., 2 parts of iodine are added, and the distillation is continued. At about evolution of more hydrochloric acid takes place, and on further heating, 310 parts of 3,4-dimethyl-hexene-(3)'-one-(2) distil at 168 C.

The portion distilling up to 100 C. is a saturated solution of hydrochloric acid. On standing, it gives a second crop of the unsaturated ketone, which can be isolated in the described manner. This process can be repeated; finally the unreacted methyl-ethyl-ketone is recovered by the customary methods. The total yield of unsaturated ketone is 500 parts, essentially equal to 100%, calculated on the ketone, which entered into the reaction.

The yield given in this example refers to an experiment carried out for 48 hours at 15 C. Under these conditions equilibrium is not yet reached; this takes at 15 C. days,- at 25 C. 4-5 days. The equilibrium lies at about 500 parts of the condensation product for 1000 parts methyl-ethyl-ketone. In the recovered portion, distilling up to 100 C. a conversion of practically the same degree is reached within the same time, in spite of the presence of a certain amount of water.

Example 2 1425 parts of methyl-ethyl-ketone are treated with 475 parts of gaseous hydrochloric acid and kept in a 'stoppered vessel at 30 C. for 4 days. 300 parts of saturated sodium chloride solution are added and the upper layer is separated, dried with anhydrous magnesium sulphate and fractionated. Up to 120 C., 195 parts (210 parts by volume) of a liquid distil over, which contain 42 parts of hydrochloric acid. At the same time 115 parts of gaseous hydrochloric acid are recovered by absorption in fresh methyl-ethyl-ketone. Then 2 parts of iodine are added and the distillation continued. 730 parts dimethyl-hexenone are thus obtained.

By distilling the aqueous layer and separating the fraction boiling up to 85 C., 377 parts of unchanged methyl-ethyl-ketone are recovered.

What I claim and desire to secure by Letters Patent is: I

1. A process for the preparation of unsaturated ketones from simple saturated ketones R2.CO.CH2.Ri in both of which R2 is an alkyl group and R1 a member of the group consisting of hydrogen and the alkyl radicals,which process consist in dissolving gaseous hydrochloric acid in an excess of the ketone at a temperature between 15 and 30 C., permitting the mixture to stand, distilling off the unchanged ketone, the water formed and the free hydrochloric acid, adding iodine to the residue and continuing the distillation.

2. A process for the preparation of unsaturated ketones.

I atom R1 o=0 Rs CO.R:

from simple saturated ketones -Rz.CO.CH2.R1 in both of which R2 is an alkyl group and R1 a member of the group consisting of hydrogen and the alkyl radicals, which process consists in dissolving gaseous hydrochloric acid'in an excess of the ketone at a temperature between 15 and 30 C., permitting the mixture to stand, distilling on the unchanged ketone, the water formed and the free hydrochloric acid, adding 0.1-1% by weight of iodine to the residue and continuing the distillation.

CHARLES WEIZMANN. 

